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| Resistors are ubiquitous. Because of this their efficiency is taken for granted, provided they are operated inside their power, voltage and environmental ratings this is affordable, given that immediately after millions of accumulated resistor-years encounter there is little left for their manufacturers to find out. But you will discover nevertheless applications where specifying and applying resistors requires to be handled with some care. Resistor forms - Surface mount chip The most popular general objective resistor may be the thick film surface mount chip variety. Accessible in substantial quantities and incredibly low costs, it really is the workhorse on the resistor world. The construction is quite uncomplicated and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations includes a resistive ink film printed or otherwise deposited on its top surface. The terminations are coated using a solder dip to make sure ease of wetting when the element is soldered into location, along with the top of the element is IBM Certified Sales Specialist coated with an epoxy or glass layer to guard the resistive element. Unique manufacturers make different claims for the ruggedness and overall performance of their parts but the standard options are comparable. Power dissipation is largely controlled by the thermal properties from the PCB pads to which the chip is soldered, and for anyone who is operating close towards the rated power with the component it is going to be necessary to confirm that your pad design agrees with the manufacturer's recommendations. You may also get metal film chip resistors for higher efficiency applications, but these are more high priced than the frequent thick film. The resistive ink method utilized for chips can also produce normal axial-lead resistors (metal glaze) of compact size, and may be employed straight onto a substrate to generate printed resistors. This technique is often employed in hybrid circuits and is extremely cost-effective mainly when large numbers of similar values are necessary. It truly is achievable to print resistors straight onto fibreglass printed circuit board, even though the outcome is of incredibly poor excellent and can't be utilised where a stable, predictable worth (compared with conventional varieties) is expected. Metal film The next most common type is the metal film, in its several guises. This really is the standard part for industrial and military purposes. One of the most well-known varieties of leaded metal film are hardly any extra pricey than carbon film and, provided their superior characteristics, especially temperature coefficient, noise and energy handling potential, numerous gear manufacturers usually do not find it worthwhile to bother with carbon film. Variants of the normal metal film cater for high or low resistance requirements. The "metal" within a metal film is actually a nickel-chromium alloy of varying composition for distinct resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the finish caps and leads are force-fitted towards the tubular assembly plus the resistance element IBM Certified Integration Developer is trimmed to value by cutting a helical groove of controlled dimensions in it, which makes it possible for exactly the same film composition to become utilised more than quite a wide range of nominal values. The entire component is then coated in epoxy and marked. The disadvantage of the helical trimming process is that it inherently increases the resistor's stray inductance, and also limits its pulse handling capability. Carbon The most frequent leaded resistor for commercial applications is definitely the carbon film. It is certainly low-cost - less than a penny in quantity. It also has the least impressive overall performance with regards to tolerance and temperature coefficient, however it is generally sufficient for general goal use. The other kind which makes use of pure carbon as the resistive element is carbon composition, which was the earliest sort of resistor but these days finds a use in specific applications which involve an assured pulse withstand capability. Wirewound For medium and high energy (higher than 2W) applications the wirewound resistor is just about universally employed. It really is pretty low cost and readily out there. Its disadvantages are its bulk, even though this makes it possible for a lower surface temperature for any offered energy dissipation; and that as a result of its construction it can be noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound forms are available either having a vitreous enamel or cement coating, or in an aluminium housing which could be mounted to a heatsink. Aluminium housings can supply energy dissipations exceeding 100W per unit. Precision resistors Once circuit requirements commence to call for accuracy and drift specifications exceeding the usual metal film abilities, the cost increases substantially. It is actually nevertheless feasible to acquire metal film resistors of "precision" overall performance as much as an order of magnitude improved than the typical, though at rates an order of magnitude or much more larger. Drift specifications of less than 10 parts-per-million per °C introduce many a lot more significant elements in to the overall performance equation, for example thermal emf, mechanical and thermal tension, and terminating resistance. These is often dealt with, plus the resistive and substrate supplies could be optimised, but the unit expenses are now measured in pounds, and delivery times stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form a lot of resistors at once, which can be then encapsulated to form a multi-resistor single package. The resulting resistors have exactly the same overall performance as a single thick film chip, though with reduced breakdown voltage and power handling capacity. Printed Circuit Passive Components Resistors are ubiquitous. Due to this their efficiency is taken for granted, supplied they're operated within their energy, voltage and environmental ratings this really is affordable, because just after millions of accumulated resistor-years knowledge there is certainly little left for their producers to discover. But there are nonetheless applications where specifying and applying resistors desires to become handled with some care. Resistor types - Surface mount chip The most widespread common goal resistor may be the thick film surface mount chip kind. Out there in massive quantities and pretty low prices, it can be the workhorse with the resistor world. The construction is really straightforward and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations features a resistive ink film printed or otherwise deposited on its top surface. The terminations are coated with a solder dip to make sure ease of wetting when the component is soldered into place, and the best in the portion is coated with an epoxy or glass layer to guard the resistive element. Distinct manufacturers make different claims for the ruggedness and efficiency of their parts however the basic options are comparable. Energy dissipation is largely controlled by the thermal properties of your PCB pads to which the chip is soldered, and in case you are running close for the rated power of your portion it will be essential to confirm that your pad style agrees with the manufacturer's recommendations. You can also get metal film chip resistors for larger overall performance applications, but these are much more high priced than the frequent thick film. The resistive ink approach utilised for chips can also produce normal axial-lead resistors (metal glaze) of modest size, and can be utilized directly onto a substrate to generate printed resistors. This technique is often made use of in hybrid circuits and is incredibly cost-effective particularly when large numbers of related values are necessary. It can be attainable to print resistors straight onto fibreglass printed circuit board, even though the result is of incredibly poor high quality and can not be used where a stable, predictable value (compared with conventional forms) is needed. Metal film The subsequent most prevalent sort will be the metal film, in its numerous guises. This is the regular part for industrial and military purposes. One of the most preferred varieties of leaded metal film are hardly any extra costly than carbon film and, provided their superior characteristics, particularly temperature coefficient, noise and power handling potential, a lot of equipment producers don't obtain it worthwhile to bother with carbon film. Variants of your common metal film cater for high or low resistance desires. The "metal" in a metal film is often a nickel-chromium alloy of varying composition for distinctive resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the end caps and leads are force-fitted for the tubular assembly as well as the resistance element is trimmed to worth by cutting a helical groove of controlled dimensions in it, which makes it possible for the identical film composition to be used more than very a wide range of nominal values. The whole element is then coated in epoxy and marked. The disadvantage of the helical trimming course of action is that it inherently increases the resistor's stray inductance, and also limits its pulse IBM Certifications handling capability. Carbon The most common leaded resistor for commercial applications is definitely the carbon film. It can be surely low cost - much less than a penny in quantity. It also has the least impressive efficiency with regards to tolerance and temperature coefficient, however it is normally sufficient for general objective use. The other sort which makes use of pure carbon because the resistive element is carbon composition, which was the earliest type of resistor but today finds a use in certain applications which involve an assured pulse withstand capability. Wirewound For medium and high energy (greater than 2W) applications the wirewound resistor is almost universally made use of. It really is pretty low-priced and readily obtainable. Its disadvantages are its bulk, although this permits a lower surface temperature for a given energy dissipation; and that because of its construction it's noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound kinds are out there either using a vitreous enamel or cement coating, or in an aluminium housing which could be mounted to a heatsink. Aluminium housings can offer you energy dissipations exceeding 100W per unit. Precision resistors Once circuit specifications get started to call for accuracy and drift specifications exceeding the usual metal film skills, the expense increases substantially. It can be still achievable to acquire metal film resistors of "precision" performance as much as an order of magnitude much better than the normal, even though at prices an order of magnitude or a lot more larger. Drift needs of much less than 10 parts-per-million per °C introduce several much more significant variables in to the efficiency equation, such as thermal emf, mechanical and thermal stress, and terminating resistance. These is usually dealt with, and the resistive and substrate materials may be optimised, however the unit fees are now measured in pounds, and delivery instances stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form lots of resistors at when, which can be then encapsulated to form a multi-resistor single package. The resulting resistors have exactly the same overall performance as a single thick film chip, though with reduced breakdown voltage and power handling ability. |
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